rates of reaction Flashcards | Knowt (2024)

Slope of the line shows

rate of reaction

steeper the slope

faster the reaction

when line becomes less steep

reaction rate is slowing down because alot of reactant molecules have already reacted to become the product so fewer molecules remain to react

when the slope is at 0 or mine is flat

reaction has stopped as all of reactant molecules have reacted

to find mean rate of reaction

quantity of product formed or reactant used/time taken

how to find rate of reaction at specific point on a curve

-draw a tangent
-construct triangle
-use change in y over change in x to find the rate

collision theory

Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy

The rate of a chemical reaction depends on

frequency of successful collisions

rate is proportional to

concentration

with a higher concentration

more product is created because more reactant molecules started

Hypothesis

a proposal that could explain a fact or observation

What is turbidity?

cloudiness

what happens when sodium thiosulfate solution is reacted with hydrochloric acid

sulfur is produced

disappearing cross experiment

-use a measuring cylinder to put 10cm^3 of sodium thiosulfate solution in a conical flask
-place flask over a printed black cross
-add equal amounts of hydrochloric acid into conical flask
-swirl solution and start stopwatch
-look down over flask
-stop clock when solution is cloudy to the point the cross is no longer visible
-carry out experiment again using lower concentration of sodium thiosulfate solution
-repeat and calculate mean values for each solution

what is the problem with the disappearing cross experiment

People have different eye sights so may get different results and it is specific to the individual

how to measure volume of gas produced by a reaction

-use a measuring cylinder to place 50cm^3 of hydrochloric acid into a conical flask
-attach flask to a bung and delivery tube
-place delivery tube into container filled with water
-place upturned measuring cylinder filled with water over delivery tube
(or use gas syringe)
-add 3cm of magnesium into conical flask and start stop watch
-every 10 seconds record volume of gas in measuring cylinder until no more is given off
-repeat experiment using different concentrations of hydrochloric acid

what happens when magnesium and hydrochloric acid react

it produces magnesium chloride and hydrogen

when surface area of a solid reactant is increased

there are more collisions per second and the rate increases

things that affect rate of reaction

temperature, pressure, surface area, concentration, catalysts

if a reactions has more reactant than product it is...

exothermic because energy must have been released from the reaction to the surroundings

activation energy

the minimum amount of energy needed to start a chemical reaction

increasing the temperature

increases reaction rate

why does increasing temperature increase rate of reaction

increases the kinetic energy of the particles so they move faster, which increases frequency of collisions and each collision has more energy to overcome the activation energy barrier more successfully

rate of reaction is what to temperature

proportional

catalysts

Chemical agents that selectively speed up chemical reactions without being consumed by the reaction

why are catalysts beneficial

they allow us to carry out reactions quickly without needing to increase temperature, which saves money and they can be reused as they aren't used up in the reaction

how do catalysts increase rate of reaction

By providing a different pathway for the reaction that has a lower activation energy

why are catalysts not included in chemical equations

they are not used up and they are not a reactant

example of a catalyst in living organisms

enzymes

what does it mean if the arrow points both ways

reversible reaction

What is a reversible reaction?

a reaction where the products can react together to form the original reactants

How can you change the direction of a reversible reaction?

change in conditions

examples of changing conditions in reversible reactions

heating, cooling

if you heat something, and are putting energy into it the reaction is

endothermic

if energy in a reaction is released and the reaction gets hot, it is

exothermjc

exothermic reaction

A reaction that releases energy in the form of heat

Endothermic reaction

A reaction that absorbs energy in the form of heat

If a reversible reaction is exothermic in one direction...

it is endothermic in the opposite direction

hydrated copper sulfate->/<-

anhydrous copper sulfate + water

Equilibrium

when the forward and reverse reactions take place at the same rate

what happens if a system is at equilibrium and a change is made to the conditions

The system responds to counteract the change

What is Le Chatelier's principle?

When a reaction at equilibrium is changed, it will seek to counteract that change

what happens if you increase the concentration of reactants or products in a reversible reaction

it is no longer at equilibrium so the concentrations of all the substances change until equilibrium is reached

what happens if you decrease the concentration of reactants or products in reversible reactions

it is no longer at equilibrium so more of the opposing side will react to form the other side so that equilibrium is reached

if you increase the temperature of a system at equilibrium

the system counteracts the change, so the equilibrium shifts to the endothermic side to reduce the temperature because it takes energy in

if you decrease the temperature of a system at equilibrium

the system counteracts the change, so the equilibrium shifts to the exothermic side so energy is released and the temperature increases

what does pressure affect

reactions involving gases

what does pressure depend on

the number of molecules in a given space

if you increase the pressure on a reversible reaction at equilibrium

the position of the equilibrium shifts to the side with the smaller number of molecules

if you reduce the pressure on a reversible reaction at equilibrium

the position of equilibrium shifts to the side with the larger number of molecules

if the number of molecules is the same on both sides

Changing pressure has no effect on the position of equilibrium

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